1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly to memory and optoelectrical devices made from colloidal-processed silicon particles.
2. Description of the Related Art
Colloidal inorganic semiconductor quantum dots (QDs)/particles are finding use as building materials in optoelectronic devices. This technology is attractive as it permits devices to be fabricated on flexible substrates by low-temperature solution-processing methods, such as spin-coating, drop-casting, and inkjet printing. At the same time, like their bulk semiconductor counterparts, semiconductor QDs/particles exhibit broadband absorption and efficient charge transport properties due to the crystalline structure of the particle core. Furthermore, resulting from the quantum confinement effect, the bandgaps of the semiconductor QDs/particles can be adjusted by simply varying the particle sizes. The smaller size leads to the higher degree of confinement and the larger bandgap. Various optoelectronic applications based on these semiconductor materials have been demonstrated and shown superior performance, including photodetectors, light-emitting diodes, and solar cells. However, these QDs/particles are usually Pb- or Cd-chalcogenide based, and are highly toxic due to their heavy metal ingredients.
Unlike compound semiconductors, silicon (Si) is biocompatible and electrochemically stable. Furthermore, owing to the needs of the microelectronics industry, Si has been well studied for the past several decades. Therefore, the development of solution-processable colloidal Si materials that retain some bulk crystalline characteristics, while achieving enhanced optical properties due to high degree of confinement, implies an interesting path of research. Extensive work has been devoted to the synthesis of Si nanoparticles, including solution-based precursor reduction or thermal decomposition, laser induced silane aerosol pyrolysis, nonthermal plasma synthesis, and etching of silicon rich oxide (SRO) thin film. However, these methods invariably require critical processing condition, special equipment, and complex purification procedures.
On the other hand, it has been reported that electrochemical etching, which only requires commercially available Si wafers, common electrolytes, and is performed in an ambient condition, can be utilized to synthesize photoluminescent porous Si nanostructures. Free standing Si nanoparticles are then prepared by pulverizing the porous Si wafers in an ultra-sonication bath. This method is especially promising for low-cost, large-quantity, high-throughput production of Si nanoparticles. Notably, by varying etching condition, not only nanoparticles but also micro-scale wires or pillars can be generated.
It would be advantageous if nano to micro-scale silicon particles could be used to fabricate optoelectronic and electronic devices, using low temperature processes that do not require expensive vacuum equipment.